A known extruded coaxial tube is manufactured in an integral manner, wherein the inner tube is rigidly joined to the outer tube by in-between spacers which are present as integral longitudinal ribs. This type of coaxial tube can be used in pneumatic servo and control systems to connect the servo and control components to spatially separate actuators. In these applications, the coaxial tube must be hermetically sealed and reliably tight with respect to the fluids, and must also be pressure-resistant. Not only must the outer tube be fluid-tight with respect to the inside, but also the inner tube must be tight with respect to the outer tube.
It is further known to use twin conduits with axially parallel constituent-tubes to load bifunctional fluid setting components, where said constituent-tubes are separated by a partition as regards the fluids while being mechanically joined.
Such twin and coaxial tubes also are being used in the automotive industry, for instance to actuate or control single-function or multi-function setting or control components which are pneumatically driven by pressure or partial vacuum. Such twin and/or coaxial tubes are especially appropriate for centralized locking systems because both the setting pressure required for the simultaneous opening and closing of vehicle doors, and the anti-theft control pressure must both be supplied.
Ever more vehicle functions are being remote-controlled electrically, pneumatically or hydraulically in automotive engineering. Consequently ever more cables, tubes and conduits are required to carry out and monitor the pertinent functions. At the same time, however, the space to pass through such cables and conduits is limited; consequently, such cables and conduits must have small radii of curvature. If the curvatures become less than a threshold defined by the elasticity of the particular material being used, hair cracks arise at the bends of the known, integrally extruded, multi-functional tubes, that is, in the known coaxial tubes and related twin conduits, from which ensue leakages and malfunctioning.
When using twin conduits, another problem arises, namely that the available sizes are insufficient with respect to vehicles for the large numbers used of conduits or tubes. The available diameter is inherently limited by design and cannot be arbitrarily enlarged.
Based on this state of the art, the object of the present invention is to create a plastic, dimensionally stable but elastically bendable coaxial tube for fluids, which can be reliably manufactured to evince good flexibility and which are tight to pressurized fluids and which furthermore also shall remain absolutely tight when being bent by small radii, as a result of which the two constituent-tubes shall be hermetically separated from each other as regards the fluids even under adverse circumstances.